\begin{table}[tbp] \centering
\newcolumntype{C}{>{\centering\arraybackslash}X}

\begin{tabularx}{\linewidth}{lCCCC}

\toprule
{Mediation variable}&{War bonds}&{Volunteers}&{Medals}&{PCA} \tabularnewline
\midrule \addlinespace[\belowrulesep]
1940 employment&--6.2\%&2.8\%&--4.6\%&--4.7\% \tabularnewline
1939 wage&6.0\%&3.1\%&0.9\%&3.4\% \tabularnewline
1940 FDR vote share&2.2\%&11.4\%&--10.7\%&--0.3\% \tabularnewline
\bottomrule 

\end{tabularx}
\end{table}
